Pokémon Omega Ruby and Alpha Sapphire add Mega-Evolutions for Steelix, Glalie - Polygon

Mega Construx Pokemon Onix Master Battle

Mega Crystal Steelix, Pokemon Wack Wiki

Steelix, Pokémon GO Wiki

Every time a Pokemon is Mega evolved, its regular Pokedex entry # Seen goes up by 1 but Caught stays the same. : r/TheSilphRoad

Elite Trainer Mark on X: Onix was Brock's first ever Pokémon. However, it didn't even evolve under his ownership, it evolved into Steelix while his brother Forrest was taking care of it.

Pokémon Sword & Shield Pokédex •

Favorite mega evolution ( sorry I messed up the first time)

Onix - XY: Evolutions Reverse Holo - Pokemon

The Master of All Kinds, Legendary, and Mega Evolution Pokémon - NEWS PAGE (1): Eeveelutions, New Dual-Type Eeveelution Discoveries For Kanto! - Wattpad

RUMOR: Let's Go! to Add New Mega Evolutions